Prior copending applications titled "Bale Density Control System" filed Feb. 28, 1978, Ser. No. 882,132 in the name of Yatcilla et al. and "Plunger Drive Connection in Bale Density Control System" filed Feb. 28, 1978, Ser. No. 882,133 in the name of Graber et al disclose and claim certain features of a hydraulic bale density control system for use in connection with extrusion-type balers. Said system involves the use of a single-acting pump mechanically associated with the plunger in such a way that during each compaction stroke of the plunger a slug of pressurized oil is added to the hydraulic control circuit so as to maintain pressure on squeeze cylinders that control the size of the discharge orifice of the bale case. If the pressure level in the circuit reaches a certain predetermined level, then a relief path is opened momentarily so as to slightly depressurize the squeeze cylinders. On the other hand, if the pressure level is not achieved, then each additional slug of oil to the squeeze cylinders increases their holding force against the forming bale as it moves through the orifice, thereby progressively increasing the density of the bale.
There is a check valve within the circuit that prevents oil from the pump from reaching the squeeze cylinders unless the pressure on the pump side of said check valve exceeds the pressure on the squeeze cylinder side of the check valve. While this check valve is a desirable part of the system for reasons which need not be elaborated upon herein, it also creates certain problems as a result of the unique way in which the baling chamber is loaded by "perfectly" prepared charges of hay having predetermined characteristics of size and density, all as explained, for example, in prior U.S. application Ser. No. 737,472 filed Nov. 1, 1976, now U.S. Pat. No. 4,106,268, in the names of White et al and titled "Method and Apparatus for Loading and Baling Crop Material".
As described, claimed and shown in said White et al application, while one charge of hay is being compacted in the baling chamber by the plunger, the next charge of material is being prepared in a loading duct adjacent the baling chamber. The optimum size and density of the charge accumulating in said duct may or may not be reached prior to the time the plunger is ready to compact the next charge. If the next charge is indeed ready, then a loader will stuff the precompressed and properly sized charge into the baling chamber ahead of the retracted plunger, whereupon the charge is compacted by the plunger in the usual way.
On the other hand, if the charge accumulating in the duct has not yet obtained the desired characteristics of size and density by the time the plunger is ready to compact that charge, then the loader is temporarily deactivated, at least for that compaction cycle of the plunger, in order to provide additional time for more material to accumulate in the duct. If the charge is ready to be loaded by the time the plunger is to commence its next compaction cycle, then the loader will indeed stuff the properly prepared charge up into the baling chamber for compaction by the plunger.
It has been noted that when the bale density control systems as disclosed in the aforementioned Yatcilla et al and Graber et al applications are incorporated into the baler of the aforementioned White et al application, temporary deactivation of the loader so that the plunger has no material to compact during its compaction stroke has the effect of giving a false indication of bale density to the control circuit to the end that additional, unneeded oil is pumped to the squeeze cylinders by the pump and plunger.
This is due to the fact that, although there is no new charge of material in the baling chamber for the plunger to engage and pack rearwardly, nonetheless the material compacted on the previous plunger stroke has sufficient resilience to bulge back into the plunger compaction area a sufficient extent that it will provide a certain amount of resistance to the plunger. If such resistance were nonexistent, then, even though oil was available from the pump to the circuit on the pump side of the earlier-mentioned check valve, the check valve would not be opened because the pressure of the circuit on the squeeze cylinder side would be considerably greater than that on the pump side. Hence, no additional oil would be added to the squeeze cylinders.
However, as is normally the case, the bulging material from the prior compaction stroke of the plunger coupled with the new slug of oil from the pump, creates sufficient resistance to raise the pressure level in the circuit on the pump side above that on the squeeze cylinder side of the check valve, thereby opening the latter and allowing the squeeze cylinders to be further pressurized by the pump.
The net effect of further pressurizing the squeeze cylinders when such additional pressurization is neither wanted or desirable is to have the cylinders substantially over-pressurized when the next charge of material is actually loaded into the baling chamber and the plunger attempts to pack the same against the overly restricted orifice. That particular compaction stroke of the plunger may result in an excessively densified portion of the bale compared to those previously compacted, and it may take several plunger strokes before the density returns down to its most desirable level. It may also allow extreme loads to the baler during this time, which are not desirable.